If you find yourself around the Capitol on Saturday afternoon and see about a thousand people running around in only their underwear, don’t worry, you’re not hallucinating. It’s also not a protest or a fraternity prank. It’s the annual Cupid’s Undie Run.

For reasons both noble and not, the flesh-filled mile is one of the season’s most popular charity events.

Now in its fourth year, participants have raised almost a million dollars for the Children’s Tumor Foundation, an organization that supports neurofibromatosis research and assists individuals and families affected by the disorder.

Pre-race festivities commence at the Pour House (319 Pennsylvania Ave. SE) and Capitol Lounge (229 Pennsylvania Ave. SE) at noon and continue long after the traffic-stopping trek has seen its final finisher.

But not to worry if this all sounds too naughty — event organizers are very careful to keep it PG-13. “We want to keep it a fun undie event versus a sexy undie event,” founder Brendan Hanrahan says. Take that how you will. Just remember: It begins and ends at a bar.